1. Field of the Invention
This invention relates generally to a velocity imaging mass spectrometer and, more particularly, to a velocity imaging mass spectrometer that includes ion focusing optics that provides velocity map imaging and deflection plates that provide a transverse velocity component to the ions that depends on their mass.
2. Discussion of the Related Art
Mass spectrometry is revolutionizing the study of complex molecules. Advances in proteomics now hinges on the central contribution of mass spectrometric methods where metabolic disease detection relies on mass spectra of blood spots. Particular challenges to current approaches include the ability to identifying and characterize a specific complex molecule in a mixture, the need for higher sensitivity and expanded dynamic range, the need for high through-put sample processing, and the ability to incorporate a variety of secondary interactions in the mass spectrometer to develop appropriate sensitive probes for the species of interest.
Of the various types of mass spectrometers, only those utilizing magnetic sector technology have been successful in the simultaneous detection of spatially resolved ions of different masses. Imaging based simultaneous detection of ions offers unique advantages over other time or frequency domain mass spectrometers, such as time-of-flight mass spectrometers (TOFMS), ion trap mass spectrometers (ITMS), and Fourier transform ion cyclotron resonance mass spectrometers (FT-ICRMS). In a spatially dispersive mode, the duty cycle of measurements can be effectively increased because of the multiplexing advantage, shot-to-shot fluctuations are minimized, and kinetic energy and mass may be measured simultaneously.
Simultaneous multiple ion monitoring at high resolution has been achieved over the years using double focusing electrostatic energy analyzer and magnetic sector mass spectrometers. However, one disadvantage of these devices is that the detector must be located at the plane of focus at the magnet exit. Detector technology development has thus played a crucial role in efforts to adapt this multiplexing ion detection capability. More recently, various types of array detectors, such as microchannel plate detector arrays, multiple-collector detector arrays, and integrated array systems, have been successfully applied with mass spectrometry for a simultaneous detection of multiple ions of different mass-to-charge values. On the other hand, little research has concentrated on developing instrumentation that exposes spatial separation as well as simultaneously multiplexing different masses beyond the magnetic sector approaches. The latter allows very high mass resolution and sensitivity at the price of expensive equipment and complicated operation.
Tandem mass spectrometry provides a system where a particular product mass is chosen out of a sample, then submitted to some chemical or physical interaction after which two mass spectrums are recorded. Tandem mass spectrometry is inherently a multi-dimensional technique. However, all current applications for tandem mass spectrometry rely on one-dimensional data recording. Because of this, tandem mass spectrometry is inherently less efficient than other spectrometric methods because the analysis includes the selection of a major mass peak, recording a fragment mass spectrum, and then iterating. However, this process further sacrifices potential correlations between parent and daughter ions that can provide additional insight and that make comparison of different spectra awkward and inconsistent.
Velocity map imaging has recently emerged as a powerful technique for simultaneous detection of a complete product velocity distribution for ions of a given mass. Velocity map imaging has also been extended to multi-mass detection strategies.